This invention relates to a cleaning apparatus for cleaning printing press plates.
Applying images to substrates by utilizing pigment or dye based ink compositions is well known in the art. These images are generally applied for the purpose of making the article more aesthetically pleasing to the consumer.
One of the difficulties historically experienced with printed substrates that are printed with pigment based ink compositions is the tendency for the ink to rub-off of the surface of the paper upon exposure of the paper to liquids. This problem is even more pronounced for printed substrates printed with inks exhibiting relatively high color densities. This problem can be further compounded when printing on absorbent disposable paper products (nonlimiting examples of which include facial tissue, bath tissue, table napkins, wipes, diapers, woven disposable fabrics, nonwovens, wovens, cotton pads, and the like). Absorbent disposable paper products tend to produce more lint and associated contaminants than other grades of paper.
One way to control ink rub-off from the surface of the printed substrate is to utilize rub resistant inks. These inks tend to adhere much better to the surface of the substrate. However, one of the drawbacks associated with using rub resistant inks relates to printing press hygiene. Inks that adhere well to the substrate often exhibit similar properties when in contact with the printing press. In particular, the print plates tend to accumulate ink and paper fiber deposits that can eventually lead to print defects in the printed substrate. In order to prevent print defects more frequent cleaning of the printing press is necessitated. This can lead to reduced printing process efficiency. This is especially true in instances where printing press production has to be halted while the printing press is cleaned. Printing press cleaning devices are generally designed to be utilized either while the press is shut down or while the press is running (i.e.; on-line cleaning).
Prior art printing press plate cleaning devices have commonly utilized air, vacuum, cleaning fluids, brushes, and other mechanical devices either individually or in combination to remove contaminants from the print plate.
It has been found that the prior art printing press plate cleaning devices can cause print defects in the printed substrate. This problem is especially magnified when the cleaning device is used for on-line cleaning on a printing press utilizing segmented printing plates. As used herein, xe2x80x9csegmented printing platesxe2x80x9d refers to printing plates which are applied in separate sections across the width of the printing press. When printing with segmented printing plates, the clearance distance between the surface of the print plate and the bottom surface of the cleaning device generally needs to be higher than when printing with sleeved printing plates. While not wishing to be bound by theory, it is believed that because of the higher clearance distance requirement between the segmented print plate and the cleaning device it is more difficult to control the rebound angle of the spent cleaning fluid (i.e.; cleaning fluid plus any contaminants such as ink, fiber, etc. removed by the cleaning fluid) from the surface of the print plate to the cleaning device. Instead of rebounding back into the cleaning device, some of the spent cleaning fluid has a tendency to rebound onto the printed substrate. As a result, it is common to observe the formation of water streaks and drops on the printed substrate.
A further drawback of prior art printing plate cleaning devices relates to the entrapment of cleaning fluid into the cells comprising the individual print plate print elements as the fluid is being applied to the surface of the print plate. The cleaning device is unable to effectively remove the spent cleaning fluid that is trapped between individual print elements of the print plate resulting in the formation of streaks and spotting on the surface of the printed substrate.
Yet a further drawback of prior art cleaning devices appears to relate to the flow dynamics of these prior art devices. Prior art cleaning devices tend to have the propensity to form recirculation zones (i.e.; zones of eddy formation) within the collection areas of these devices. These zones can potentially interfere with the collection of the spent cleaning fluid thereby inhibiting the efficient removal of the spent fluid. The spent cleaning fluid is then free to fall back onto the surface of the print plate and/or the substrate after initially entering the cleaning apparatus. These recirculation zones can also cause the cleaning apparatus to plug.
The cleaning apparatus of the present invention addresses these drawbacks as it can be utilized at higher clearance distances without the formation of water streaks and drops on the printed substrate. Furthermore, the cleaning apparatus of the present invention penetrates the boundary layer of air associated with the surface to be cleaned resulting in efficient cleaning.
Yet further, the cleaning apparatus of the present invention is able to effectively remove spent cleaning fluid trapped between individual print elements of the print plate. Even yet further, the cleaning apparatus of the present invention minimizes recirculation zones within the device thereby providing more efficient collection of the spent cleaning fluid. In addition, the cleaning apparatus of the present invention tends to be self-cleaning. The benefits of the present invention include improved process efficiency and reliability.
The present invention relates to a cleaning apparatus. The cleaning apparatus comprises a plenum and a head connected to the plenum. The head includes: a nozzle, at least two banks of air jets wherein at least one bank of air jets is offset from a second bank of air jets and at least three vacuum ports. The nozzle may be positioned inside one of the vacuum ports. The head may also be positioned outboard of the vacuum ports. The local velocity within a substantial portion of the head and plenum is greater than the conveying velocity of the largest cleaning fluid droplet.
The cleaning apparatus may also include an aerodynamic surface. The aerodynamic surface may surround the interior surface of the cleaning apparatus. The aerodynamic surface may surround the interior of the head, the plenum, or a combination of both.
The cleaning apparatus includes at least one vacuum port and at least one bank of air jets. One or more of the vacuum ports may include a partition. The partition can separate the vacuum port from the bank of air jets. The partition can include a beveled edge. The beveled edge oriented in the upward direction of air flow. The beveled edge can comprise an angle of greater than about 0xc2x0 but less than or equal to about 45xc2x0.
The cleaning apparatus can also optionally include an anti-plate stripping element.